The average daily number of COVID-19 cases in the United States reached more than 267,000 on Tuesday, a record largely due to a variant of the ultra-transmissible coronavirus that experts are still working to understand.
The current seven-day average of 267,305 daily cases has surpassed the previous record of around 250,000 cases, set in early January 2021. And the current vertical increase in cases is expected to continue in the weeks to come.
“The rapid increase in cases that we are seeing across the country is largely a reflection of the exceptionally transmissible omicron variant,” said Dr Rochelle Walensky, director of the Centers for Disease Control and Prevention, during a briefing. press at the White House Wednesday.
Omicron was first detected in the United States just four weeks ago on December 1. And although he arrived in the midst of a raging wave of the highly transmissible delta variant, omicron quickly overthrew delta to become the dominant variant in the United States. According to the latest genomic data, the CDC estimates that omicron represented about 59 percent of all cases nationwide during the week ending December 25. And cases are now up 60% from the previous week.
“In just a few short weeks, the omicron has grown rapidly across the country and, we expect it to continue to circulate in the coming weeks,” Walensky added.
As the omicron continues to rise, scientists are still working to collect data on the variant, particularly with regard to the resistance of current vaccines and tests and the severity of omicron infections.
For vaccines, data to date continues to indicate that omicron can avoid immune defenses generated by vaccines and past infections. But the booster doses appear to restore protection to delta-era levels.
For the severity of the disease, all data continues to suggest that omicron is less severe than previous variants. But it’s still unclear whether this is because omicron is inherently less virulent or whether many people have less severe disease because they have pre-existing immunity from the vaccination and / or previous infection. or a combination of inherent viral qualities and prior immunity.
Several laboratory studies in rodent models have suggested that omicron may be very effective at replicating quickly in the upper respiratory tract, but less effective at infecting the lower lungs where serious disease can set in.
Researchers in South Africa recently reported striking hospital data comparing previous waves to the current wave of omicron. Hospital deaths fell from 21.3% to 4.5%. Admissions to intensive care units fell from 4.3% to 1%. Patients requiring supplemental oxygen fell from 99% to 45%. And the average length of hospital stays fell from 8.8 days to four days.
But the omicron wave patients were younger – an average age of 39 compared to an average age of 49 in previous waves. Younger people tend to have milder illness in general.
At the press conference, leading infectious disease specialist Anthony Fauci also pointed out that researchers in South Africa attributed the lighter presentations to a “high level of previous infection and, to some extent, vaccine coverage.” in the population.
Fauci went on to note that similar trends appear to be developing in the UK, and even here in the US. “The peak in cases [in the US] is disproportionate to the increase in hospitalizations, ”he noted with caution. “So if you look at the fourteen-day averages, last night’s data shows a more than 126% increase in cases and an 11% increase in hospitalizations.”
This may be due, in part, to the fact that hospitalizations and deaths are still lagging behind. And the increase in omicron is relatively new. “However, the pattern and the disparity between cases and hospitalizations strongly suggest that there will be a lower hospitalization-to-case ratio when the situation becomes clearer,” Fauci said.
Another aspect of the omicron situation that is not yet clear is the role of rapid tests. On Tuesday, the United States Food and Drug Administration released a vague statement noting that current rapid tests on the market are able to detect omicron, but “may have reduced sensitivity”. We do not know what this means in concrete terms. The FDA also said rapid tests may have only reduced sensitivity when trying to detect a live virus. When the researchers used an inactivated virus, rapid tests were just as good at detecting omicron as they were at detecting delta and other variants. The agency has not released any details or additional data on the experiments conducted and the individual rapid tests evaluated.
Rapid tests often detect the core protein of SARS-CoV-2 viruses, not the spike protein, where most of the omicron mutations of concern are found. The core protein tends to mutate less in general, and omicron carries only a few mutations in this protein.
Last week, the UK’s Health Security Agency published a technical briefing saying he had evaluated five rapid tests in the market for their ability to detect the omicron variant. The agency used the lab-grown omicron virus from clinical samples. They found no reduction in the performance of rapid tests against omicron.
“In summary, the [rapid tests] evaluated, which all target the core protein, detected the new omicron variant which contains four amino acid changes from the original viral sequence, ”concludes the technical report. “This does not affect their performance in the lab and we will be monitoring more variations as they arise as part of our ongoing evaluation program.”
Test the questions
During the White House press conference today, Fauci questioned the FDA’s vague announcement, saying it was motivated by transparency and not to raise doubts about the testing.
“What the FDA was saying: When they looked at the sensitivity versus omicron, in some of the tests there seemed to be some decrease – not disappearance, but decrease – in sensitivity,” Fauci said. . “The fact that the sensitivity is somewhat diminished does not eliminate the importance… and the usefulness of these tests in different circumstances. That was the message from the FDA. They wanted to make sure that they were completely transparent in saying that the sensitivity might drop a bit, but they pointed out that there is still significant use for these tests. “
Adding even more confusion, Walensky noted at another point in the press conference that the CDC did not recommend rapid tests to end periods of isolation. The CDC shortened the recommended isolation period this week for asymptomatic people who test positive for COVID-19 from 10 days to five days, with five additional days of masking. But the new guidelines do not include a recommendation that people wait negative for a rapid test to end isolation sooner, which some experts considered “unwise.”
Walensky defended the updated guidelines, arguing that rapid tests five days after infection may not “give a good indication of transmissibility.” In other words, rapid tests can be sensitive enough to stay positive once a person is no longer contagious.
“On the other hand, we know that after five days people are much less likely to transmit the virus and that masking further reduces that risk,” Walensky added. “And that’s why people have to mask themselves for five days after their five days of isolation.”
While the performance of the rapid tests is still unclear, Walensky stressed that they are intended for serial use. People at risk or at risk of developing COVID-19 should take several rapid tests over several days.
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